A Hierarchical Approach to the Treatment of Ventricular Tachycardias

Electrical management of ventricular tachycardias with an implanted device is greatly complicated by reduced hemodynamic tolerance to the tachycardia with increasing rate, and by the risk of accelerating the tachycardia into fibrillation. Pacing (extrastimuli, bursts), low-energy cardioversion, and high-energy defibrillation therapies are all useful in safely treating a ventricular tachycardia. A implantable device is described which allows the classification of up to four different arrhythmias each having their own detection criteria (including high rate, sudden onset, rate stability and sustained high rate). For each classified arrhythmia, up to four, therapies may be programmed to be sequentially delivered. This scheme allows for increasing on the aggressiveness of the therapy based on elapsed time, increased rate, or both; and provides a large amount of flexibility for tailoring the desired therapies to individual patients.     

SOME EFFECTS OF ISOFLURANE ON I WAVES OF THE MOTOR EVOKED POTENTIAL

We have investigated the effects of isoflurane anaesthesia onthe motor evoked potential recorded in the extradural spaceduring corrective spinal surgery in 15 patients. Isofluranewas added to a nitrous oxide in oxygen mixture supplementedwith fentanyl and a neuromuscular blocking agent. Isofluranewas administered to achieve end-tidal concentrations of 2%,1 % and 0% in all patients, and also of 1.5% and 0.5% in ninepatients. Transcranial electrical stimulation of the motor cortexwas used to elicit descending volleys in corticospinal axons(the motor evoked potential). With stimuli of 450-750 V andno isoflurane, multiple I waves were always seen following theD wave. In all patients the number of I waves decreased andindividual I waves became smaller in amplitude the greater theisoflurane concentration, but there were only minor changesin the D wave. The greatest depressant effect on I waves occurredat an end-tidal concentration of 0.5%. Given that I waves arean index of synaptic transmission, anaesthetic-induced changesin I waves may provide a useful model for the neuronal eventsunderlying anaesthesia-induced unconsciousness.     

Review: The Effect of Contact Lens Wear on the Electrophysiology of the Corneal Epithelium

ABSTRACT The effect of contact lens wear on the electrical characteristics of the corneal epithelium is reviewed. Both soft and hard lenses reduce the transcortical potential, with hard lenses having a greater effect. Recovery of the potential is slower following hard contact lens wear. This paper suggests that hard contact lenses cause more disruption to the electrical resistance and electromotive forces in the corneal epithelium. The mechanisms are discussed using an electrical circuit model of the cornea.     

Alterations in membrane electrical properties during long-term denervation of rat skeletal muscle

Some membrane electrical properties of the extensor digitorum longus muscle of the rat were examined up to 21 days after denervation. The resting potential was significantly more depolarized at 3 days after denervation than it was at later times. The rate of rise (dV/dt) of the action potential decreased throughout the time course of the study but approached a steady value between 14 and 21 days after denervation. In addition, the dV/dt of tetrodotoxin (TTX)-resistant action potentials increased up to and including 7 days after nerve section, but declined thereafter. When expressed as % of control, the dose-response to TTX was similar throughout denervation. It is suggested that the large depolarization observed early in denervation may be related to the turnover of membrane constituents occurring at this time. The results also suggest that denervation produces a reduction in the number of fast TTX-sensitive Na⁺ channels with the appearance of a new population of slow TTX-resistant channels. However, long term denervation results in a reduction in the density of both types of channels.     

The performance of ultraviolet lights used to polymerize fissure sealants

The performances of ultraviolet (uv) lights used to initiate polymerization in fissure sealant systems were studied with a view to establishing recommendations for improving clinical results. The relationship between the setting time of an uv polymerized sealant (Nuva-seal) and the intensity of radiation applied was first established. This was compared with the intensity and distribution of radiation from seven Nuva-lites and one Quartzlite. It was found that some of the Nuva-lites did not produce an average intensity of uv radiation sufficient to completely polymerize Nuva-seal within the manufacturer's recommended exposure times. It is suggested that this may be a factor contributing to the large variation in sealant retention found in the different clinical trials with Nuva-seal. Finally, a number of recommendations are made to ensure that sufficient uv radiation is applied to all sealant surfaces when the Nuva-seal system is used.